Environmentally compatible hydraulic fluid

ABSTRACT

Environmentally safe and compatible fluids that are useful as lubricants, and especially as hydraulic fluids, in mobile machinery are formulated to be non-contaminating when accidentally contacted with surrounding vegetation, and removable from vegetation by simply washing the vegetation with tap water. The fluids of the invention are polyalkylene glycol-based and having an ethylene oxide to propylene oxide ratio of from about 68:32 to about 78:22.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of patent application Ser. No. 11/414,690 filed Apr. 28, 2006 which claims priority to provisional patent application Ser. No. 60/696,060 filed Jul. 1, 2005. The disclosure of each of these related applications is incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to hydraulic fluids for use in machinery and other mechanical systems, and is especially directed to hydraulic fluids for use in machinery that is used in outdoor environments where the unintentional dispersal of hydraulic fluid from such machinery will not harm the surrounding vegetation or the environment.

2. Description of Related Art

It has been a particular problem that machinery used for various outdoor purposes has a tendency to leak hydraulic fluid into the surrounding environment. Conventional petroleum-based hydraulic fluids are well known to have deleterious effects on the environment, such as killing vegetation and polluting the ground and ground water.

Of particular concern in this regard is machinery used to groom golf courses or commercial garden areas, and equipment or machinery used in or near environmentally sensitive areas (e.g., boats, ships, bridges, etc.). When conventional hydraulic fluid from motors, mowers, earth movers and other equipment leaks from the machinery onto the grass or garden areas, or into aquatic environments, the hydraulic fluid contaminates the vegetation and cannot be washed off. The vegetation dies within a short period of time thereafter, and re-seeding or re-planting cannot take place for several weeks to months after contamination. In the interim, the areas where the vegetation died off are unsightly.

An accidental spill of hydraulic fluid from a machine on a golf course damages the turf, and, the volume of hydraulic fluid spilt per square inch corresponds to the length of time surrounding grass will take to cover over a damaged area. Hydraulic spills in excess of 0.10 ml/inch² of fluid on turf will result in necrosis of the plant. The average spill occurs at a rate of 0.9 ml/inch² with 9% being catastrophic at a rate of 1.5-1.85 ml/inch².

When a spill in the vicinity of 0.5-0.9 ml/inch occurs on a green, the green becomes unplayable and repair costs run in the thousands of dollars. In some instances it can take up to 3 months to recover from a minor spill and in severe cases where the fluid spills onto the turf at a rate above 1.0 ml/inch², it is necessary to re-sod the damaged area.

When spills occur, the common clean up procedure is to wash the area of contaminated turf with water containing a surfactant (soap). The majority of the time, this approach is not effective, but merely disperses the fluid over a wider area, increasing the damage. In a only a minority of cases, such as when the volume of fluid spilt on the turf is less than 0.1 ml/inch², does washing a spill with surfactant resolve the issues. The alternative method of cleaning a spill is by layering charcoal powder over fluid contaminated turf has a similarly low rate of success.

In recognition of this problem, other fluid materials have been used as a replacement for conventional petroleum-based hydraulic fluids. For example, vegetable or plant-based oils (i.e., non-petroleum-based oils) have been used in machinery. However, such oils are either unsuitable for use as hydraulic fluids due to the demands of the machinery, and/or such substitute fluids still prove to be damaging to the vegetation because they cannot be easily washed off and although biodegradable are still toxic to the plant, causing necrosis when spilled thereon. Many non-petroleum oils have similar physical properties to petroleum-based products. For example, both have limited solubility in water, both create slicks on water and both form emulsions and sludges. Additionally, non-petroleum oils tend to be persistent and remain in the environment for long periods of time. Thus, non-petroleum or vegetable-based oils are not necessarily compatible with the environment.

Therefore, it would be advantageous to provide a fluid material that is highly suitable for use as hydraulic fluid in machinery that is used in environmentally-sensitive areas such that if the fluid leaks from the machinery, the fluid will be environmentally compatible (i.e., non-destructive to vegetation) and not contaminate and/or kill the vegetation.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, a fluid is provided for use as a lubricant or hydraulic fluid in machinery, the fluid being environmentally friendly to vegetation and the surrounding area. The fluid, if leaked or spilled from the machinery onto vegetation, can be washed off with tap water without any deleterious effects on the vegetation and without contamination of the surrounding environment.

The hydraulic fluid of the present invention comprises a polyalkylene glycol-based fluid of selected viscosity which renders the fluid very suitable for use as a lubricant or hydraulic fluid for machinery (e.g. mobile machinery, such as mowers, earth movers, etc.). The polyalkylene glycol used in the present invention is water soluble, thereby rendering the fluid easily removable from vegetation or other surfaces by simply washing the surface that is exposed to the fluid.

In a particularly suitable embodiment of the invention, the biocompatible fluids of the invention are comprised of one or more water-soluble polyalkylene glycols and the composition has an ethylene oxide to propylene oxide ratio of between about 68:32 and about 78:22. The biocompatible fluids may comprise a mixture of two or more polyalkylene glycols having varying ethylene glycol contents, ethylene oxide to propylene oxide ratios, molecular weights and viscosities.

The fluid of the present invention may further include a third polyalkylene glycol that is preferably polyethylene glycol with a selected viscosity. The biocompatible fluids of the invention may also include at least one surfactant. The fluid of the present invention may further contain other elements, including but not limited to antioxidants, non-corrosion or non-rusting agents, extreme pressure (EP) and antiwear (AW) additives and additional additives of a type used in formulation of lubricants and hydraulic fluids.

In one illustrative embodiment, the present invention provides a hydraulic fluid which does not detrimentally damage turf when an accidental spill occurs, which meets OEM specifications for a hydraulic fluid, such as ISO 46 grade hydraulic fluid, with a minimum pour point of −30° F., a viscosity of not less than 9.0 cst at 100° C. Such a fluid may include the common performance additives required to make a premium anti-wear hydraulic fluid, such as anti-foam, anti-wear, corrosion inhibition and extreme pressure additives. It may also only contain a maximum of 1000 ppm water to meet the specifications for anhydrous hydraulic fluids.

DETAILED DESCRIPTION OF THE INVENTION

The environmentally compatible lubrication or hydraulic fluids of the present invention are generally polyalkylene glycol-based, where the polyalkylene glycol is water-soluble. Polyalkylene glycols include a class of compounds comprising polymers of alkylene oxides and mixtures or derivatives of alkylene oxides. Polyalkylene glycols may be low molecular weight or high in molecular weight, and vary widely in viscosity characteristics. The polyalkylene glycols of the present invention may have an ethylene glycol content of between about 50% to about 80%, may be comprised of a selected ethylene oxide to propylene oxide (EO:PO) ratio and have a selected molecular weight and viscosity.

In particular, the water-soluble polyalkylene glycols used in the environmentally compatible fluids of the present invention have varied ethylene oxide to propylene oxide ratios, but the fluid compositions most suitably have an ethylene oxide to propylene oxide ratio of from about 68:32 to about 78:22 in order to render the fluids of the composition most environmentally compatible. The polyalkylene glycols used in the fluid compositions of the invention may have an SUS (Saybolt Universal Seconds) viscosity of from about 50 to about 800, while the compositions may have an SUS viscosity of from about 200 to 240. Further, the polyalkylene glycols used in the present invention may have a molecular weight of from about 200 to about 1700.

In a particularly suitable embodiment of the environmentally compatible fluids of the present invention, the polyalkylene glycol-based component of the fluid may comprise at least two polyalkylene glycols having varied EO:PO ratios, viscosities and molecular weights. While the EO:PO ratio may vary between the one or more polyalkylene glycols mixed in the fluid, the overall ratio of EO:PO of the fluid remains from about 68:32 to about 78:22 to provide optimal biocompatibility of the fluid. Examples of polyalkylene glycols that may be used in the present invention are poly-glycols made by BASF (Florham Park, N.J.) and identified as the Plurasafe® WS series and Plurasafe® WT series.

In addition to the polyalkylene glycol or glycols, the environmentally compatible fluids may also contain polyethylene glycol (PEG). The PEG used may preferably have a viscosity of from about 89 to 106 SUS at 40° C. An example of a suitable PEG for use in the invention is Pluracol E200 manufactured by BASF. Other PEG's are equally suitable for use, however.

The environmentally compatible fluids may contain additional elements that render the fluid suitable for use as a lubricant or hydraulic fluid in machinery, and which also render the fluid environmentally compatible with the environment. For example, the fluid may contain one or more suitable surfactants. Non-ionic, anionic, amphoteric and cationic surfactants, or mixtures thereof, may be suitable for use. Most suitably, the surfactant may be non-ionic. One exemplar surfactant for use in the environmentally compatible fluids is a poloxamer, such as polyoxypropylene, polyoxyethylene blocked copolymer. An exemplar blocked copolymer that is suitable for use in the invention is either Pluronic L31 or Pluronic R 17R4, both available from BASF.

Additional components for use in the fluids of the invention may include anti-corrosion and/or anti-rusting agents, antioxidants and EP/AW additives, and mixtures thereof. Exemplar anti-corrosion agents may include lanolin, silica-based agents, molybdenum sulfide, boron amine derivatives and benzotriazole or benzotriazole-based compounds. Exemplar antioxidants may include trimethyl quinoline derivatives. Exemplar EP/AW additives may include amine phosphates, thiadiazole derivatives and organosulfur-phosphorous compounds.

A general formula for an environmentally-safe fluid of the present invention is as follows:

Example I

Component % by weight Polyalkylene glycol 50-85 Surfactant 2.0-6.0 Antioxidant 0.1-2.0 Anti-corrosion or anti-rust agent 0.01-2.0 

where the polyalkylene glycol of the fluid composition has an EO:PO ratio of from about 78:22 to about 68:32.

The following example illustrates a more specific embodiment of the environmentally compatible fluid of the of present invention:

Example II

Component % by weight Polyalkylene glycol “A” 50-85 Polyalkylene glycol “B” 10-35 Polyoxypropylene, polyoxyethylene blocked copolymer 2.0-6.0 Irganox L57 0.1-1.0 Benzotriazole 0.01-0.1  Amyl acid phosphate 0.4-2.0

where polyalkylene glycol “A” has a minimum ethylene glycol content of 75% and SUS (Saybolt Universal Seconds) viscosity of about 450. An exemplar polyalkylene glycol “A” of this type is available from INEOS Oxide (Zwijndrecht, Belgium) and is identified as PAG 75-H Series. The polyalkylene glycol “B” has an ethylene glycol content of 50% and may preferably have an SUS viscosity of from about 55 to 660. Examples of suitable polyalkylene glycol “B” materials are manufactured by BASF (Florham Park, N.J.) and are in the Plurasafe WS Series. The combined polyalkylene glycol “A” and “B” has an EO/PO ratio of from about 78:22 to about 68:32. The polyoxypropylene, polyoxyethylene blocked copolymer is a difunctional blocked copolymer, non-ionic surfactant. An exemplar product of this class is available from BASF from the Pluronic R series. The Irganox® L57 is an alkylated di-phenyl amine antioxidant propriety to Ciba Chemicals (Basel, Switzerland), and is used in various lubricants. Benzotriazole is an anti-corrosion or anti-rusting agent that is manufactured by various companies, and is available from Cobratec Metal Protection (PMC Specialties Group, Inc., Sun Valley, Calif.) and is sold under the brand name Cobratec® 99. Amyl acid phosphate is an exemplar EP additive and is available from many companies, including Polaquima, S.A. DE CV (Mexico City, Mexico).

A further formulation of Example II above may be as follows:

Example III

Component % by weight Polyalkylene glycol “A” 70 Polyalkylene glycol “B” 26 Polyoxypropylene, polyoxyethylene blocked copolymer 3.24 Irganox L57 0.20 Benzotriazole 0.04 Amyl acid phosphate 0.5

A further embodiment of the environmentally compatible fluids of the present invention is as follows:

Example IV

Component % by weight Polyalkylene glycol “A” 58 Polyalkylene glycol “B” 14 Polyalkylene glycol “C” 23.95 Polyoxypropylene, polyoxyethylene blocked copolymer 3. Irganox L57 0.36 Irgalube 349 0.15 Amyl acid phosphate 0.50 Benzotriazole 0.04

where polyalkylene glycol “A” has an ethylene glycol content of about 70% and an EO:PO ratio of about 70:30; polyalkylene glycol “B” has an ethylene glycol content of about 50% and an EO:PO ratio of about 50:50; polyalkylene glycol “C” is a polyethylene glycol (PEG) with a viscosity of between 89 and 106 SUS; and Irgalube 349 is an EP/AW additive and corrosion inhibitor manufactured by Ciba Chemicals.

Other exemplar formulations of the environmentally compatible fluids of the present invention are as follows:

Example V

Component % by weight Polyalkylene glycol “A” 40 Polyalkylene glycol “B” 11 Polyalkylene glycol “C” 45 Polyoxypropylene, polyoxyethylene blocked copolymer 3.0 Irganox L57 0.31 Irgalube 349 0.15 Amyl acid phosphate 0.50 Benzotriazole 0.04

where polyalkylene glycol “A” has an EO:PO ratio of 50:50 an SUS viscosity of about 450; polyalkylene glycol “B” has an EO:PO ratio of about 50:50 and an SUS viscosity of about 55; polyalkylene glycol “C” is a PEG having a viscosity of between 89 and about 106 SUS and the blocked copolymer is non-ionic.

Example VI

Component % by weight Polyalkylene glycol “A” 60 Polyalkylene glycol “B” 14 Polyalkylene glycol “C” 22 Polyoxypropylene, polyoxyethylene blocked copolymer 3.0 Benzotriazole 0.04 Irganox L57 0.31 Irgalube 349 0.15 Amyl acid phosphate 0.50

where polyalkylene glycol “A” has an EO:PO ratio of between about 70:30 and 80:20, and an SUS viscosity of about 450; polyalkylene glycol “B” has an EO:PO ratio of about 50:50 and an SUS viscosity of about 55; polyalkylene glycol “C” is a PEG having a viscosity of between about 89 and 106 SUS and the blocked copolymer is non-ionic.

Example VII

Component % by weight Polyalkylene glycol “A” 51 Polyalkylene glycol “B” 23 Polyalkylene glycol “C” 22 Polyoxypropylene, polyoxyethylene blocked copolymer 3.0 Benzotriazole 0.04 Irganox L57 0.31 Irgalube 349 0.15 Amyl acid phosphate 0.50

where polyalkylene glycol “A” has an EO:PO ratio of between about 70:30 and 80:20, and an SUS viscosity of about 450; polyalkylene glycol “B” has an EO:PO ratio of about 50:50 and an SUS viscosity of about 100; polyalkylene glycol “C” is a PEG having a viscosity of between about 89 and 106 SUS and the blocked copolymer is non-ionic.

Example VIII

Component % by weight Polyalkylene glycol “A” 74 Polyalkylene glycol “B” 22 Polyoxypropylene, polyoxyethylene blocked copolymer 3.0 Benzotriazole 0.04 Irganox L57 0.31 Amyl acid phosphate 0.65

where polyalkylene glycol “A” has an EO:PO ratio of between about 70:30 and 80:20, and an SUS viscosity of about 450; polyalkylene glycol “B” has an EO:PO ratio of about 50:50 and an SUS viscosity of about and the blocked copolymer is non-ionic.

Each of the formulations described above are prepared by mixing the polyalkylene glycol or polyalkylene glycols together with the surfactant or surfactants and stirring the mixture until clear and bright (i.e., not cloudy and free of particulates). The remaining constituents or elements are then added and stirred together. The resulting mixture is heated to a maximum temperature of 50° C. for about 30-60 minutes until any solids, such as may be added in the form of the benzotriazole, are dissolved into solution. Blending of the materials should be continued until a homogeneous clear and bright fluid is achieved.

Example IX Development of Biodegradable Fluid Formulas Meeting Industry Standards and Comparative Testing Against Known Hydraulic Fluids

A number of different commercially available hydraulic fluids were tested from vegetable based, synthetic based (polyalphaoleophins, polyalakylene glycols, esters) to white mineral based oils to determine if any of the fluids would not cause necrosis of the turf plant. All fluids tested including those listed as biodegradable, damaged the crown and roots of the turf thereby causing necrosis of the turf plant when spilt at a rate of 0.50 ml/inch² on the grass and washed with water. All of the commercially available fluids tested, including the biodegradable fluids, were thus found to be toxic to the turf in conditions corresponding to a typical spill situation.

The commercially available hydraulic fluids tested included fully formulated PAG hydraulic fluids having about 50:50 EO:PO ratios and one fluid had a 60:40 EO:PO ratio, all of which were toxic to the turf.

Also tested was a PAG base fluid, identified as WT 400, which had a EO:PO ratio of about 75:25. Unlike the commercially available hydraulic fluids, the WT400 fluids' effects on the turf were minimal and full recovery occurred within 2-4 days. The addition of a surfactant, (Pluronic L31/R17R4) lowered the recovery to within 1-2 days.

From these test results, it was determined that a PAG base fluid with a EO:PO ratio of between 68:32 to 78:22 is not toxic to the grass, and that as the PO value increases, the fluid becomes increasingly toxic to the turf plant.

Based on these results, an ISO 46 grade base fluid (41.4-50.6 cst at 40° C.) was made using WT400, but this fluid did not meet the required OEM specifications for the pour point or the required viscosity at 100′C. The pour point for this fluid was found to be 0° F., well above the required minimum of −30° F. Thus, although acceptable when spilt on the turf, it could not be used as a hydraulic fluid in the lawn maintenance equipment as it did not meet the required OEM specifications.

In order to meet OEM specifications as well as too not damage turf, it was necessary to develop a formulation for an ISO 46 grade hydraulic fluid with an EO:PO ratio of 75:25 by weight, that had a pour point of less than −30° F. and a viscosity of greater than 9.0 cst at 100° C.

A fluid with this specification was created by applicant by blending three base fluids in the manner previously described herein. These first base fluid is a polyalkylene glycol having an EO:PO ratio of about 50:50 by weight with a viscosity of about 100 cst at 40° C. This base fluid has an acceptable pour point and a high viscosity at 100° C. The use of this first base fluid allows the final product to meet the required viscosity at 100° C. The first base fluid is present in an amount of from about 40 to about 70 percent by weight in the exemplary formulation. In one illustrative example, a hydraulic fluid in accordance with the present invention contains about 51% of the first base fluid.

The second base fluid is a polyalkylene glycol stock having a EO:PO ratio of about 50:50 by weight with a viscosity of about 8 cst at 40° C. The second base fluid is used to lower the viscosity of the final base fluid and to lower pour point. The third base stock, is PEG of about 100% EO which is used to get the correct EO:PO ratio of between about 68:32 to about 78:22 by weight. In the illustrative embodiment, the final EO:PO ratio is about 72:28 by weight. Use, of this third base stock is critical as it is the only way to achieve the required EO:PO ratio while still meeting the rest of the OEM specifications.

Blending these three based fluids in the correct ratio resulted in a final fluid that meets all of the OEM specifications. Addition of a surfactant of from about at 2% to about 3.5% of volume, was found to assist in removing the hydraulic fluid off the plants' leaves. When this formulated hydraulic fluid was tested by spilling on the turf at a rate of 1.85 ml/inch² and washed with water, no detrimental impact on the turf was found.

As with the prior examples, these formulations may be prepared by mixing the polyalkylene glycols together with the surfactant or surfactants and stirring the mixture until clear and bright (i.e., not cloudy and free of particulates). The remaining constituents or elements, including the various additives, are then added and stirred together. The resulting mixture may be heated to a maximum temperature of 50° C. for about 30-60 minutes until any solids are dissolved into solution. Blending of the materials should be continued until a homogeneous clear and bright fluid is achieved.

The OECD 301 B test (Modified Sturm procedures as set forth in OECD GUIDELINE FOR TESTING OF CHEMICALS, No. 301 Ready Biodegradability Adopted by the Council on 17 Jul. 1992, Organisation for Economic Co-operation and Development, the contents of which are incorporated by reference herein) is used to determine the rate of the biodegradation of a hydraulic fluid. Using a standard 28 day protocol, the biodegradation determination of a hydraulic fluid is determined within a 10 day window. Hydraulic fluids are classified based on the 301-B test results as either Readily Biodegradable (at least 60% of the sample oil is degraded within the 10 day window), Inherently Biodegradable (20-60% of the sample oil is degraded within the 10 day window), or Persistent (less than 20% of the sample oil is degraded within the 10 day window). Prior PAG based hydraulic fluid's that meet the ISO 46 grade have only been able to be classified as Inherently Biodegradable in the biodegradability test OECD 301 B. The hydraulic fluid of this Example IX is classified as Readily Biodegradable.

The use of the second and third base stocks having viscosities lower than 35 cst allows fluids in accordance with the present invention to be classified as readily biodegradable as these two base fluids have biodegradation rates of over 90% and therefore the final fluid easily exceeds the 60% biodegradation requirement of the OECD 301 B test. Similarly, these exemplary fluids also achieves the status of readily biodegradable for the OECD 301 F standard.

It is also commonly known that fully formulated Polyalkylene Glycol hydraulic fluids only pass the ASTM 665A corrosion test. By using amyl acid phosphate as an additive, hydraulic fluids in accordance with the present invention pass the ASTM 665A corrosion test and the ASTM 665B corrosion test.

The environmentally compatible fluids of the present invention may be used as a lubricant for any number of purposes, but is particularly useful as a hydraulic fluid in mobile machinery. When used as a hydraulic fluid in machinery, especially machinery such as mowers and earth movers, and the like, any leaked or accidentally spilled fluid may be easily washed from vegetation with tap water. The vegetation is not contaminated by the fluid and will not be killed by the fluid. The environmentally compatible fluids of the present invention may be adapted to any number of uses as lubricants for any variety of machinery or metal usage. Therefore, reference herein to specific examples and formulations of the invention are by way of example only and not by way of limitation. 

1. An environmentally compatible lubrication and hydraulic fluid for machinery, comprising: a polyalkylene glycol base comprised of two polyalkylene glycols having different viscosities, which is characterized in that the ethylene oxide to propylene oxide ratio of the polyalkylene glycol component of the fluid is from between about 68:32 and 78:22 by weight, and polyethylene glycol in an amount by weight of between 22.0% and 45.0%.
 2. The environmentally compatible lubrication and hydraulic fluid of claim 1 wherein one of the two polyalkylene glycols having different viscosities comprises a polyalkylene glycol having an EO:PO ratio of about 50:50 by weight with a viscosity of about 100 cst at 40°, in an amount of from about 40.0% to about 70.0%.
 3. The environmentally compatible lubrication and hydraulic fluid of claim 2 wherein the one of said two polyalkylene glycols having different viscosities comprises a polyalkylene glycol having an EO:PO ratio of about 50:50 by weight with a viscosity of about 100 cst at 40°, in an amount of from about 51.0%.
 4. The environmentally compatible lubrication and hydraulic fluid of claim 2 wherein one of said two polyalkylene glycols having different viscosities comprises a polyalkylene glycol having an EO:PO ratio of about 50:50 by weight with a viscosity of about 8 cst at 40° C.
 5. The environmentally compatible lubrication and hydraulic fluid of claim 2 wherein the ethylene oxide to propylene oxide ratio of the polyalkylene glycol component of the fluid is about 72:28.
 6. The environmentally compatible lubrication and hydraulic fluid of claim 2 further comprising at least one surfactant.
 7. The environmentally compatible lubrication and hydraulic fluid of claim 6 further comprising a surfactant in an amount of from about at 2% to about 3.5%.
 8. The environmentally compatible lubrication and hydraulic fluid of claim 6 wherein said at least one surfactant is a polyoxypropylene, polyoxyethylene blocked copolymer.
 9. The environmentally compatible lubrication and hydraulic fluid of claim 6 wherein said surfactant is selected from the group consisting of non-ionic, anionic, cationic and amphoteric surfactants, and mixtures thereof.
 10. The environmentally compatible lubrication and hydraulic fluid of claim 1 further comprising at least one antioxidant, anti-corrosive or EP/AW additive, or combinations thereof.
 11. The environmentally compatible lubrication and hydraulic fluid of claim 10 wherein said fluid contains an EP/AW additive comprising amyl acid phosphate.
 12. A method of producing an environmentally compatible lubrication and hydraulic fluid for machinery, the method comprising: combining a first base fluid comprising a polyalkylene glycol having an EO:PO ratio of about 50:50 by weight and a viscosity of about 100 cst at 40° C. and a second base fluid comprising a polyalkylene glycol having a EO:PO ratio of about 50:50 by weight and a viscosity of about 8 cst at 40° C.; and adding a third base fluid comprising PEG of about 100% EO to reach a desired final EO:PO ratio of between about 68:32 to about 78:22 by weight.
 13. The method according to claim 12, wherein combining a first base fluid comprising a polyalkylene glycol having an EO:PO ratio of about 50:50 by weight and a viscosity of about 100 cst at 40° C. with a second base fluid comprising a polyalkylene glycol having a EO:PO ratio of about 50:50 by weight and a viscosity of about 8 cst at 40 comprises adding the first base fluid in an amount of from about 40 to about 70 percent by weight of the final fluid.
 14. The method according to claim 13, wherein adding the first base fluid an amount of from about 51 percent by weight of the final fluid.
 15. The method according to claim 12, wherein adding a third base fluid comprising PEG of about 100% EO to reach a desired final EO:PO ratio of between about 68:32 to about 78:22 by weight comprises adding the third base fluid to reach a desired final EO:PO ratio of about 72:28 by weight.
 16. The method according to claim 12, wherein the first base fluid, the second base fluid and the third base fluid are mixed by adding the three base fluids together and stirring until a homogeneous fluid is achieved.
 17. The method according to claim 16, further comprising heating the resulting mixture to a maximum temperature of 50° C. for about 30-60 minutes to dissolve any any solids into solution.
 18. The method according to claim 12, further comprising adding at least one surfactant comprising a polyoxypropylene, or polyoxyethylene blocked copolymer.
 19. The method according to claim 12, further comprising adding at least one surfactant is selected from the group consisting of non-ionic, anionic, cationic and amphoteric surfactants, and mixtures thereof.
 20. The method according to claim 12, further comprising adding at least one antioxidant, anti-corrosive or EP/AW additive, or combinations thereof. 